1. Field of the Invention
The present disclosure generally relates to the fabrication of semiconductor devices, and, more particularly, to a substrate resistor with an overlying gate structure.
2. Description of the Related Art
The fabrication of advanced integrated circuits, such as CPU's, storage devices, ASIC's (application specific integrated circuits) and the like, requires the formation of a large number of circuit elements in a given chip area according to a specified circuit layout. Field effect transistors (NMOS and PMOS transistors) represent one important type of circuit element that substantially determines performance of such integrated circuits. During the fabrication of complex integrated circuits using, for instance, MOS technology, millions of transistors, e.g., NMOS transistors and/or PMOS transistors, are formed on a substrate including a crystalline semiconductor layer. A field effect transistor, whether an NMOS or a PMOS device, is a planar device that typically includes a source region, a drain region, a channel region that is positioned between the source region and the drain region, and a gate structure positioned above the channel region. The gate structure is typically comprised of a very thin gate insulation layer and one or more conductive layers that act as a conductive gate electrode. In a field effect transistor, the conductivity of the channel region, i.e., the drive current capability of the conductive channel, is controlled by applying an appropriate voltage to the gate electrode.
In modern integrated circuits, a very high number of individual circuit elements, such as field effect transistors in the form of CMOS, NMOS, PMOS elements and the like, are formed on a single chip area. In addition to the large number of transistor elements, a plurality of passive circuit elements, such as capacitors, resistors and the like, are typically formed in integrated circuits that are used for a plurality of purposes, such as for decoupling.
To improve process integration, it is useful to use similar structures for forming different types of devices. For example, if structures that are used in the formation of transistors can also be used to fabricate resistors, the processing efficiencies may be increased. Polysilicon lines may be used in the fabrication of transistors as gate electrodes. A resistor may also be created using a polysilicon line. The resistance of a polysilicon resistor is determined essentially by its length and cross-sectional area. It is difficult to provide resistors with varying resistance in an array of parallel resistors. In addition, the amount of current that can be carried by a polysilicon resistor is limited due to Ohmic heating. If the current passing through the resistor is sufficiently high, a rupture may occur, resulting in a change to the resistance value or an open circuit (similar to a fuse).
The present disclosure is directed to various methods and resulting devices that may avoid, or at least reduce, the effects of one or more of the problems identified above.